Method for manufacturing an electrically connectable module

ABSTRACT

An electrically connectable module is manufactured from a substrate of an electrically insulating polymer matrix doped with an electrically insulating fibrous filler capable of heat conversion to an electrically conductive fibrous filler to form a fiber-doped substrate. One end of an electrical connector is embedded in the fiber-doped substrate to locate the one end adjacent the surface of the substrate while exposing an opposite end of the electrical connector. The surface of the fiber-doped substrate is locally heated preferably with a laser to form a conductive trace by the in-situ heat conversion of the electrically insulating fibrous filler, the localized heating including the one end of the electrical connector to electrically connect the electrical connector to the conductive trace. In another embodiment, a conductive material is electrodeposited on the conductive trace by applying a voltage to the opposite end of the electrical connector. The substrate is molded into a desired shape to form the module, and a plurality of electrical connectors can be embedded into the substrate in any one of several different standardized arrangements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electrically connectable module and a methodfor manufacturing same in which an electrical connector is embedded in asubstrate of an electrically insulating polymer matrix doped with anelectrically insulating fibrous filler capable of heat conversion to anelectrically conductive fibrous filler. Localized heating of thesubstrate adjacent the electrical connector produces a conductive traceformed in the substrate and forms an electrical connection between thepre-embedded electrical connector and the conductive trace. Moreparticularly, the invention relates to an electrically connectablemodule and a method of making it, in which an electrical connection isformed between one end of an electrical connector (previously embeddedin a polymer matrix) and a laser-produced conductive trace formed in thepolymeric substrate, for the dual purposes of using the electricalconnector for electrodepositing a conductive material onto theconductive trace and for subsequent electrical connection to an externalelectrical component.

2. Discussion of Related Art

In electrical machines such as image reproducing devices, it isnecessary to distribute power and/or logic signals to various siteswithin the machine. Traditionally, this has taken the form of usingconventional wires and wiring harnesses in the machine to distribute thepower and logic signals to the various functional elements in themachine.

As an alternative to wires, it is known to use a CO₂ laser to burnconductive traces in a polymeric material that has been doped withcarbon fibers so that the untreated material (not subjected to thelaser) is not conductive. When locally heated by the laser, thepolymeric material volatilizes to leave a conductive network of polymerresidue and conductive dopant. U.S. Pat. No. 4,841,099 teaches how anelectrically insulating polymer matrix is filled with an electricallyinsulating fibrous filler capable of heat conversion to an electricallyconducting fibrous filler, to form a continuous electrically conductivepath by the in-situ heat conversion of the electrically insulatingfibrous filler using a laser. The entire disclosure of U.S. Pat. No.4,841,099 is herein incorporated by reference.

In order to make the conductivity of the traces more sufficient for manyapplications, it has been proposed that metal be electrodeposited ontothe traces. One advantage of this electrodepositing approach is to placemetal conductors onto the polymeric material in the trough or channelcreated by the laser with the metal adhering to the polymeric material.However, the prior art has not developed or suggested methods forreliably electroplating the trace, or for connecting the traces toelectrical connectors in the polymeric material for distributing poweror signals between the trace and an external component.

U.S. Pat. No. 4,604,678 to Hagner discloses a circuit board plated withhigh density electrical traces connected to respective terminals of anumber of electrical current components mounted on a substrate. Grooveson the substrate can be machined by a laser. The components areassembled before the grooves are plated to minimize production costs andassure electrical connection between the plated laser-formed grooves andthe terminals of respective components. The conductive traces overlieand are in electrical contact with chip pads.

U.S. Pat. No. 3,984,620 to Robillard et al. discloses an integratedcircuit chip test and assembly package having a semiconductorinterconnection substrate with apertures for integrated circuits. Theassembly package includes an interconnection with external leads whichare located between insulating layers of the substrate.

U.S. Pat. No. 3,818,279 to Seeger, Jr. et al. discloses an electricalinterconnection and contacting system comprising a flexible plasticinsulator, most preferably an elastomeric substrate having at least onelayer of electrically conductive elastomeric material embedded therein.The system is useful in coupling integrated circuits to other circuitry.

SUMMARY OF THE INVENTION

It is thus a feature of the invention to provide an electricallyconnectable module and a method for manufacturing same, in which anelectrical connector pre-embedded into the module is electricallyconnected to a conductive trace upon formation of the conductive traceon a surface of the module.

Another feature of the invention is to reliably electroplate aconductive trace formed in a polymeric material by localized laserheating.

It is another feature of the invention to reliably connect theconductive trace to an electrical connector embedded in the polymericmaterial.

According to one aspect of the present invention, a method ofmanufacturing an electrically connectable module from a substrate of anelectrically insulating polymer matrix comprises the steps of: dopingthe substrate with an electrically insulating fibrous filler capable ofheat conversion to an electrically conductive fibrous filler, to form afiber-doped substrate; and embedding one end of an electrical connectorin the fiber-doped substrate to locate the one end adjacent a surface ofthe substrate while exposing an opposite end of the electricalconnector. The surface of the fiber-doped substrate is then locallyheated preferably with a laser to form a conductive trace by the in-situheat conversion of the electrically insulating fibrous filler, includingthe localized heating at the one end of the electrical connector toelectrically connect the electrical connector to the conductive trace.

According to another aspect of the present invention, the opposite endof the electrical connector is then used to apply a voltage to theconductive trace for electrodepositing a conductive material on theconductive trace.

In accordance with another aspect of the invention, an electricallyconnectable module comprises a substrate formed from an electricallyinsulating polymer matrix doped with an electrically insulating fibrousfiller capable of heat conversion to an electrically conductive fibrousfiller; an electrical connector embedded into the substrate and havingone end adjacent a surface of the substrate and an opposite end exposedfrom the substrate; a continuous electrically conductive trace formed onthe surface of the substrate by in-situ heat conversion of theelectrically insulating fibrous filler; and a connection formed betweenthe one end of the electrical connector and the conductive trace by thein-situ heat conversion of the electrically insulating fibrous filler inthe polymer matrix surrounding the one end of the electrical connector.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the invention will be describedin detail with reference to the following figures wherein:

FIG. 1A is a side view of a molded component doped with carbon fibersand having embedded electrical connectors;

FIG. 1B is a top view of the component of FIG. 1A;

FIG. 2A is a plan view of one surface of a fiber-doped chip carrierhaving embedded electrical connectors;

FIG. 2B is a side view of the chip carrier of FIG. 2A illustrating theembedded electrical connectors having one end extending to an uppersurface of the carrier and an opposite end projecting from the lowersurface of the carrier; and

FIG. 2C is a plan view of the upper surface of the chip carrier of FIG.2B illustrating the conductive traces connected to the ends of theelectrical connectors.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with preferred embodiments of the invention and asillustrated in FIGS. 1A, 1B, 2A, 2B and 2C, an electrical connector 10is embedded in a substrate S which is preferably an electricallyinsulating polymer matrix material molded to a desired shape. Thedisclosure of U.S. Pat. No. 4,841,099 (which is herein incorporated byreference) describes the polymer materials. One end 12 of the connector10 is buried at or just below the surface 14 of the polymer, while theopposite end 16 is exposed from the molded polymeric material. After theprocess described below, the opposite or exposed end 16 will beavailable for electrical connection to a component external to themolded polymeric material.

The substrate S has been doped with an electrically insulating fibrousfiller capable of heat conversion to an electrically conductive fibrousfiller. Typical fibrous fillers are petroleum pitch based carbon fiberswhich are heat convertible carbonaceous fibers, such as thermallystabilized, polyacrylonitrile fibers which upon heat conversion provideelectrically conducting fibers (also known as preox fibers as disclosedin U.S. Pat. No. 4,841,099). Localized heating of the surface 14 of thefiber-doped substrate S with a laser forms conductive traces 20. Thedisclosure of U.S. Pat. No. 4,841,099 (which is incorporated byreference) describes the materials and processes for doping the fibersin the substrate and forming the conductive traces.

In accordance with the invention, the localized heating to form theconductive trace 20 includes localized heating at the buried end 12 ofthe connector to volatilize the thin layer of polymeric material aroundthe electrical connector 10, thus guaranteeing that the conductive fibertrace 20 will make electrical contact with the one end 12 of theconnector 10. The localized heating can begin or end at the buried end12 of the connector 10 when forming the trace 20. Accordingly, theelectrical connector 10 is preembedded in the fiber-doped polymericmaterial and the electrical connection between the electrical connectorand the conductive trace is formed simultaneously with the formation ofthe conductive trace by starting or ending the localized laser heatingat the buried end 12 of the electrical connector.

After electrical connection to the trace, the electrical connector 10can be used as a reliable connection to the laser buried trace forelectrodeposition (which is cheaper than electroless deposition) of aconductive material (preferably copper) onto the trace. In particular, avoltage can be applied to the exposed end 16 of the electrical connector10 to apply the voltage to the conductive trace for electrodeposition.The process of electrodeposition of conductive materials onto the traceis well known to those skilled in the art as evidenced by U.S. Pat. No.4,841,099.

FIGS. 1A and 1B and FIGS. 2A, 2B and 2C show two exemplary electricallyconnectable modules using the teachings of the present invention. Thesubstrate S is prepared by molding into the desired shape, for examplethe prong arrangement of FIGS. 1A and 1B, or a standard chip carrierarrangement of FIGS. 2A, 2B and 2C. U.S. Pat. No. 841,099 disclosesmolding techniques. The substrate S is doped with carbon fibers andembedded with the electrical connectors 10. In FIGS. 1A and 1B, theelectrical connectors 10 are prongs having their buried ends 12 adjacentthe surface 14 of the module on which the traces will be formed. Theopposite end 16 is exposed. In FIGS. 2A, 2B and 2C, the electricalconnectors 10 are pins which have their buried ends 12 adjacent thesurface 14 on which the conductive traces 20 will be formed with thepins extending to the opposite surface.

The conductive trace 20 is then formed on the surface S of the substratewith a laser, preferably by starting at the buried end 12 of theelectrical connector 10 to connect the electrical connector 10 to thetrace 20. Using the exposed end 16 of the electrical connector 10 toapply a voltage, the conductive material is electrodeposited on thelaser trace 20. The electrical connector 10 is now used for connectionto the trace 20 when the module is assembled into the machine. Theelectrical connections such as the prongs of FIGS. 1A and 1B or the pinsof FIGS. 2A, 2B and 2C can be arranged in different standardized formsor predetermined arrangements for ease of connection to variouselectrical components. For example, in FIGS. 1A-1B, the prongarrangement can accept a similar female style connector. In FIGS. 2A,2B, and 2C, the arrangement of pins accepts a carrier for an integratedcircuit. It is also noted that the polymer provides mechanical supportto the electrical connectors which allows rigid connections to be madewhen two polymer pieces are connected together. For example, twoconnector modules can be made in the manner described herein with maleand female style connectors, respectively, which can then bemechanically connected together by standard methods to automaticallyelectrically connect the modules together.

As an example, a standard four pin connector was embedded into a plasticpart (the plastic part being a low cost molding material includingpolyphenylene oxides known as General Electric Noryl™, and the plasticpart being doped with preox fibers in an amount of about 30% by weightof the total filled polymer matrix) with the pins extending through theplastic to the other side. The module formed of the embedded connectorand polymer matrix material can be manufactured and processed by any ofthe methods and examples of U.S. Pat. No. 4,841,099. A poor electricalconnection between the pins and the conductive traces resulted if theburied ends of the pins were too deep into the plastic part or stuck toofar out of the plastic part. Optimum results were achieved when the topof each pin was flush with the surface of the plastic part. Also, whenburning the trace in the plastic part, a higher laser power (by about30%) helped to make a better electrical connection between the pins andthe laser burnt trace.

After the laser traces were made and rinsed with a solvent to removeresidue, the resistance between a pin and the trace was about 200 ohms.This is equivalent to the resistance of a few inches of the laser tracein the plastic and was found not to limit electrodeposition of copperonto the traces. Traces were easily pated to a resistance of less thanan ohm with a few hours of electroplating. Better morphologies wereobtained in the electrodeposited copper if the deposition started onlyon the laser trace (keeping the connector pins out of the platingsolution initially). This allowed a good conducting path to be made inthe laser trace to reduce the potential drop along the trace whichpromoted preferential deposition on the pin rather than on the lasertrace.

The invention has been described with reference to its preferredembodiments which are intended to be illustrative and not limiting.Various changes may be made by those skilled in the art withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

What is claimed is:
 1. A method of manufacturing an electricallyconnectable module from a substrate of an electrically insulatingpolymer matrix, the method comprising the steps of:doping the substancewith an electrically insulating fibrous filler capable of heatconversion to an electrically conductive fibrous filler, to form afiber-doped substrate; embedding one end of an electrical connector intothe fiber-doped substrate to locate the one end adjacent a surface ofthe substrate while exposing an opposite end of the electricalconnector; and locally heating the surface of the fiber-doped substrateto form a continuous electrically conductive trace by the in-situ heatconversion of the electrically insulating fibrous filler including thelocalized heating at the one end of the pre-embedded electricalconnector to electrically connect the electrical connector to theconductive trace.
 2. The method of claim 1 further comprising the stepof electrodepositing a conductive material on the conductive trace byapplying a voltage to the opposite end of the electrical connector. 3.The method of claim 2, wherein the conductive material is copper.
 4. Themethod of claim 2, wherein the conductive material is electrodepositedinitially only on the conductive trace.
 5. The method of claim 2,wherein the step of electrodepositing the conductive material onto theconductive trace includes the step of filling the conductive materialinto a channel created by the localized heating during formation of theconductive trace.
 6. The method of claim 2, wherein the step ofelectrodepositing the conductive material on the conductive traceincludes the step of adhering the conductive material to the substrate.7. The method of claim 1, wherein the one end of the electricalconnector is located flush with the surface of the substrate.
 8. Themethod of claim 1, wherein the one end of the electrical connector islocated below the surface of the substrate.
 9. The method of claim 1,wherein the conductive trace and connection between the conductive traceand the one end of the electrical connector are formed by volatilizingthe polymer matrix in the substrate and the polymer matrix surroundingthe one end of the electrical connector.
 10. The method of claim 1further comprising the step of conducting electrical power through theconductive trace by connecting the opposite end of the electricalconnector to an electrical component.
 11. The method of claim 1 furthercomprising the step of conducting electrical power through theelectrical connection by connecting the conductive trace to anelectrical component.
 12. The method of claim 1 further comprising thestep of molding of the substrate into the desired shape prior to thelocalized heating of the substrate.
 13. The method of claim 1, wherein aplurality of electrical connectors are embedded into the fiber-dopedsubstrate in a standardized arrangement, each electrical connector beingconnected to a corresponding conductive trace for electrical connectionof the electrical connectors and conductive traces to an electricalcomponent.
 14. The method of claim 1 wherein the step of localizedheating includes using a laser to form the conductive trace.
 15. Amethod of manufacturing an electrically connectable module from asubstrate of an electrically insulating polymer matrix, the methodcomprising the steps of:doping the substrate with an electricallyinsulating fibrous filler capable of heat conversion to an electricallyconductive fibrous filler, to form a fiber-doped substrate; embeddingone end of an electrical connector into the fiber-doped substrate tolocate the one end adjacent a surface of the substrate while exposing anopposite end of the electrical connector; locally heating the surface ofthe fiber-doped substrate to form a continuous electrically conductivetrace by the in-situ heat conversion of the electrically insulatingfibrous filler including the localized heating at the one end of thepre-embedded electrical connector to electrically connect the electricalconnector to the conductive trace; and applying a voltage to theopposite end of the electrical connector to apply a voltage to theconductive trace for electrodepositing a conductive material on theconductive trace.
 16. The method of claim 15, wherein the conductivematerial is copper.
 17. The method of claim 15, wherein the conductivematerial is electrodeposited initially only on the conductive trace. 18.The method of claim 15, wherein the step of electrodepositing theconductive material onto the conductive trace includes the step offilling the conductive material into a channel created by the localizedheating during formation of the conductive trace.
 19. The method ofclaim 15, wherein the step of electrodepositing the conductive materialon the conductive trace includes the step of adhering the conductivematerial to the substrate.
 20. The method of claim 15, wherein the oneend of the electrical connector is located flush with the surface of thesubstrate.
 21. The method of claim 15, wherein the one end of theelectrical connector is located below the surface of the substrate. 22.The method of claim 15, wherein the conductive trace and connectionbetween the conductive trace and one end of the electrical connector areformed by volatilizing the polymer matrix in the substrate and thepolymer matrix surrounding the one end of the electrical connector. 23.The method of claim 15 further comprising the step of conductingelectrical power through the conductive trace by connecting the oppositeend of the electrical connector to an external electrical component. 24.The method of claim 15 further comprising the step of conductingelectrical power through the electrical connection by connecting theconductive trace to an electrical component.
 25. The method of claim 15further comprising the step of molding of the substrate into the desiredshape prior to the localized heating of the substrate.
 26. The method ofclaim 15, wherein a plurality of electrical connectors are embedded intothe fiber-doped substrate in a standardized arrangement, each electricalconnector being connected to a corresponding conductive trace forelectrical connection of the electrical connectors and conductive tracesto an electrical component.
 27. The method of claim 15 wherein the stepof localized heating includes using a laser to form the conductivetrace.